Complaints can occur because users, in many e-mail programs, can report an e-mail as spam by clicking a special button.

These so-called feedback loop complaints are anonymously transmitted to promio.net by providers, such as Hotmail, Yahoo, AOL, 1&1 every time a receiver marks a mailing as spam. Depending on the unsubscribe method selected, the user is added to the e-mail blacklist or if they are in use, added to the corresponding block list or unsubscribed from newsletter.